Eddy current speed reducer

ABSTRACT

An eddy current braking apparatus according to the invention comprises: a brake disk ( 2 ) connected to a rotary shaft ( 1 ); a plurality of permanent magnets ( 7 ) arranged so that magnetic pole surfaces are opposed to the brake disk ( 2 ); and a drive mechanism for moving the permanent magnets ( 7 ) toward and away from the brake disk ( 2 ). Preferably, it further comprises a guide sleeve ( 3 ) supported by a nonrotatable structural section not connected to the rotary shaft ( 1 ), which receives a support ring ( 4 ) supporting the permanent magnets ( 7 ) and is arranged facing to the brake disk ( 2 ). Moreover, in the guide sleeve ( 3 ), there are provided ferromagnetic members ( 8 ) positioned opposite to the brake disk ( 2 ). Alternatively, the whole of said guide sleeve ( 3 ) including an end face opposed to said permanent magnets ( 7 ) is constructed of nonmagnetic material.

TECHNICAL FIELD

The present invention relates to an eddy current braking apparatus whichassists a main brake installed in a vehicle or the like, and relatesspecifically to an eddy current braking apparatus using a disk typebrake member.

BACKGROUND ART

Braking apparatus for vehicles such as trucks and buses include, inaddition to primary braking apparatus such as foot brakes and auxiliarybraking apparatus such as exhaust brakes, eddy current braking apparatuswhich reduce speed in a stable manner, and also prevent the foot brakefrom burning out, in such situations as when descending long slopes.

FIG. 4 is a diagram showing the structure of an eddy current brakingapparatus as proposed in Japanese Examined Patent Publication No. Hei.6-81486, which shows an example of a method in which the polar surfaces(magnetic pole surfaces) of permanent magnets are in an opposedrelationship to a rotary drum type braking member. The presentspecification may describe this method, in which the polar surfaces(magnetic pole surfaces) of the permanent magnets oppose the brakemember, as simply the “opposing magnet pole surface method”.

In the example shown in FIG. 4, inside the rotary drum 11 are provided asupport ring 4 which holds permanent magnets 7 in a circle, and a drivemechanism 5 for moving the support ring 4 towards the inner peripheralsurface of the rotary drum 11. Moving the support ring 4 towards therotary drum 11 causes braking torque to be produced in the rotary drum.

In the specific structure of this braking apparatus, a nonmagnetic ring12 is disposed inside of the rotary drum 11, and a plurality offerromagnetic members 8 are arranged around the nonmagnetic ring 12 inthe circumferential direction. Inside the nonmagnetic ring 12, thesemicircular support ring 4 is guidably supported so as to be movable inthe radial direction. The permanent magnets 7 are coupled to the supportring 4 so as to oppose the ferromagnetic members 8, and the ends of thearc shaped support ring 4 are connected by piston rods 6 attached to apair of fluid pressure actuators 5. When the pair of upper and loweractuators 5 are actuated, the permanent magnets 7 move towards theferromagnetic members 8, and magnetic lines of force are exerted on theinner peripheral surface of the rotary drum 11, generating brakingtorque.

However, the eddy current braking apparatus shown in FIG. 4 entails manyproblems, categorized as problems caused by the use of a rotary drum,and problems caused by employing the “opposing magnet pole surfacemethod”. First, a serious problem caused by the use of a rotary drum isthat because the stator (guide sleeve) which houses the permanentmagnets and the like is covered by the inner peripheral surface of therotary drum, heat dissipation is poor, and the heat generated duringactuation causes marked expansion. Details on the problems caused bythis factor are described below.

On the other hand, problems caused by employing the “opposing magnetpole surface method” can be attributed to the moving of the support ringwhich arranges the permanent magnets closer to the inner peripheralsurface of the rotary drum using the fluid pressure actuators. In otherwords, in the proposed braking apparatus, the structure is such that thepermanent magnets cannot be disposed on part of the inner circumferenceof the rotary drum, which makes it difficult to secure the necessarybraking force. Moreover, the length of the magnetic circuit formed bythe permanent magnets may lengthen, and the magnetic circuit may beinterrupted at a part of the inner peripheral surface, which reducemagnetic efficiency. Furthermore, because this structure does not allowthe permanent magnets to be disposed perpendicularly relative to therotary drum and in an evenly spaced manner, a large stroke must be usedto move the permanent magnets back to a non-braking position.

As described above, an eddy current braking apparatus using a rotarydrum has problems with heat dissipation during braking, inherent in itsstructure. Specifically, heat generated in the rotary drum duringbraking causes expansion of the outer peripheral section. In order toabsorb this expansion, a system of drum support that is complex indesign is required, which complicates the drum sturucture. In addition,because the rotational weight is concentrated towards the outside in theradial direction, it is difficult to adjust the rotational balance, andthe excessive stress caused by centrifugal force causes such problems asa reduction in durability and a tendency for dimensional variation.

Incidentally, by adjusting the distance between the permanent magnetsand the rotary drum inner peripheral surface, it is possible to adjustthe braking torque, but to adjust the air gap it is necessary to enlargeand reduce the inside diameter of the rotary drum. This means that theability to use the components of the rotary drum as common parts islost.

Consequently, recently, instead of drum type apparatus which use arotary drum, a great number of disk type eddy current braking apparatushave been proposed (for example Japanese Unexamined Patent PublicationNo. 2000-35835, Japanese Unexamined Patent Publication No. 2001-28876).

FIG. 5 shows an embodiment of a disk type eddy current braking apparatusproposed in Japanese Unexamined Patent Publication No. 2001-28876. Asshown in the figure, in this braking apparatus, permanent magnets 7 aredisposed on the side face of a magnet support ring 4, so that themagnetic pole direction of the permanent magnets 7 is aligned with theradial direction. The permanent magnets 7 are disposed so that thepolarity of the outer surfaces of the permanent magnets 7 alternates inthe circumferential direction. The base ends of a pair of magnetic polemembers 8 oppose the outer surface and inner surface of each permanentmagnet 7, and the ends of the magnetic pole members 8 are bentdiagonally so that the side faces oppose the brake disk 2. Eddy currentcaused by the magnetic field from the permanent magnets 7 is generatedin the brake disk 2, producing braking force. On the other hand, in anon-braking state, in this structure the permanent magnets 7 areretracted, producing a shorted magnetic circuit between shortingcylinders 10 which sandwich the permanent magnets 7, and thus no longerexerting a magnetic field on the brake disk 2.

However, in the eddy current braking apparatus shown in FIG. 5, becausethe magnetic circuit is oblique during braking, the magnetic circuitlengthens, which increases the likelihood of a short in the magnetism.This results in deterioration in the magnetic efficiency. In addition, apredetermined gap is required between the ferromagnetic members 8 whichoppose both pole surfaces of the permanent magnets 7, and as the air gapin the magnetic circuit increases, the magnet field acting on the brakedisk is dispersed in the radial direction. This also results in adeterioration in magnetic efficiency.

In addition, in the eddy current braking apparatus described above,during non-braking, the permanent magnets 7 must be retracted to theposition of the shorting cylinders 10, so as to be withdrawn completelyaway from the ferromagnetic members 8. As a result, if the dimensions ofthe permanent magnets are increased to obtain a large amount of brakingforce, the stroke required for the permanent magnets to be retractedwhen changing from a braking to a non-braking state (referred to simplyas the “switching stroke” below) must be larger. As a result, thebraking apparatus itself must be larger, and a greater length of time isrequired to switch braking states.

In accordance with the above circumstances, it is an object of thepresent invention to provide an eddy current braking apparatus whichwhile simple in structure has excellent braking efficiency.

Furthermore, another object is to provide an eddy current brakingapparatus which has a small switching stroke and is capable of rapidswitching.

DISCLOSURE OF INVENTION

In order to achieve the above objects, the eddy current brakingapparatus according to the present invention comprises: a brake diskconnected to a rotary shaft; a plurality of permanent magnets arrangedso that magnetic pole surfaces are opposed to the brake disk; and adrive mechanism for moving the permanent magnets toward and away fromthe brake disk.

As described above, because with this system the permanent magnetsoppose the brake disk and are moved towards it to generate brakingtorque in the disk itself, the magnetic lines of force of the permanentmagnets can be applied to the brake disk with a short magnetic pathlength. Consequently, the magnetic resistance of the magnetic circuit isminimized, and the efficiency of braking torque generation is improved.As a result of the improved braking efficiency, comparatively smallpermanent magnets can be used, which allows a lighter, more compact andlower cost apparatus.

Preferably, the present invention further comprises a guide sleevesupported by a nonrotatable structural section, which receives thesupport ring and is disposed facing the brake disk. In the guide sleeve,it is possible to provide ferromagnetic members positioned facing thebrake disk. Alternatively, the whole including the end face of the guidesleeve opposed to the permanent magnets is constructed of nonmagneticmaterial.

As a result of varied investigation into both drum type and disk typebraking apparatus, the inventors made the following findings (a) to (c)below regarding a lightweight and compact eddy current brakingapparatus:

(a) With a disk type apparatus, a structure can be used which has theguide sleeve (stator) exposed to the outside of the disk which generatesthe heat, and this allows excellent heat dissipation. Accordingly, thishas an advantage in that a reduction in braking force due to a rise inthe magnet temperature within the guide sleeve tends not to occur.Furthermore, because cooling fins are attached to a flat disk, theconfiguration design is also simple.

(b) With a drum type eddy current braking apparatus, if the drum reachesa high temperature during braking, with a drum type apparatus the drumwill expand in the radial direction, increasing the distance between thepermanent magnets or ferromagnetic members (pole pieces) and the drum.In other words, the air gap enlarges and as a result braking force isreduced. On the other hand, with a disk type eddy current brakingapparatus, there is no variation in the air gap even if the disk expandsin the radial direction, and such an eddy current braking apparatustherefore has excellent fade characteristics (the phenomenon wherebybraking force reduces along with braking time). Furthermore, in order toadjust the braking force by increasing or decreasing the initial airgap, in a drum type apparatus it is necessary to machine (enlarge theinternal diameter to increase the air gap) or remake the drum. On theother hand, in a disk type apparatus, it is possible to increase ordecrease the air gap simply by adjusting the position of the disk in therotary shaft direction, and therefore the braking force can be adjustedeasily while leaving most components unchanged.

(c) Disks are durable (have burst resistance), inspecting and repairingthe heating surface is easy, and ease of maintenance is also excellent.In other words, if the need to repair a disk arises due to fatigue orthe like, it is possible to reuse the disk after simple maintenance, forexample facing of the disk surface, giving excellent recyclability.

Therefore, a disk type structure is used for the eddy current brakingapparatus of the present invention. Accordingly, the apparatus of thepresent invention has excellent heat dissipation, easy braking torqueadjustment, and excellent maintainability and recyclability.

Furthermore, the present invention applies the “opposing magnet polesurface method” to a disk type eddy current braking apparatus. As aresult the apparatus of the present invention enables the magnetic linesof force of the permanent magnets to be applied directly to the brakedisk with a short magnetic path length, and therefore improves theefficiency of braking torque generation.

FIG. 3 is a diagram showing the relationship between the magneticattraction of the brake disk when not rotating (braking state) and theswitching stroke in the present invention. The switching stroke iscalculated from the distance between the magnetic pole surface of thepermanent magnets which faces the brake disk and the end face of theguide sleeve which opposes this magnetic pole surface. A load cell formeasuring the attraction is provided between a joint section joining thecylinder rod end and the magnet support ring. The attraction isdetermined by the load cell after changing the switching stroke byinserting a shim inside of the cylinder.

As shown in FIG. 3, the magnetic attraction attenuates along the curvefor the (−n)th power of the distance, from the end face of the guidesleeve. Accordingly, if a switching stroke of 10 mm to 30 mm is secured,it is possible to switch between braking and non-braking states. Inother words, the attraction during braking is approximately 2000 kgf,but securing a switching stroke of 10 mm to 30 mm means that themagnetic lines of force from the permanent magnets do not reach thebrake disk, and magnetic leakage is no longer a problem. That is, withthe present invention, the switching stroke from a position where thepermanent magnets are near to and facing the brake disk, at whichbraking is possible, to a non-braking position away from the brake disk,can be short. In this manner, with the eddy current braking apparatus ofthe present invention, the length of the switching stroke can beshortened to approximately 10 to 30 mm, and this allows the apparatus tobe smaller and the switching speed to be faster.

Accordingly, the following is an example of structure of a first aspectof the present invention. The eddy current braking apparatus comprises:a brake disk connected to a rotary shaft; a guide sleeve supported by anonrotatable section and disposed beside the brake disk; a support ringhoused inside this guide sleeve and movable in the rotary shaftdirection; a plurality of permanent magnets arranged opposed to thebrake disk around the circumferential direction of the support ring, andso that adjacent magnet poles are opposite; and ferromagnetic membersdisposed on the end face of the guide sleeve so as to face the permanentmagnets, in a configuration which allows the permanent magnets to movefreely from a position near to and facing the brake disk, at whichbraking is possible, to a non-braking position away from the brake disk.

Even with eddy current braking apparatus which use permanent magnets,compared to a drum type apparatus in which the guide sleeve is coveredby the drum which is the source of heat, with a disk type apparatus astructure can be used in which the guide sleeve is exposed to outside ofthe brake disk which is the source of heat, and therefore the heatdissipation of the guide sleeve itself is excellent. In other words,assuming the same amount of heat introduced into the guide sleeve, in adisk type apparatus the guide sleeve can contact the open air directly,effectively increasing the area available for cooling, which allowstemperature rise within the guide sleeve to be controlled better than ina drum type apparatus.

In addition, by using a disk type structure for the apparatus, it iseasier to attach cooling fins than in a drum type structure, and theheat dissipating performance of the brake disk, which is a source ofheat generation, can be improved. Accordingly, the inventors of thepresent invention investigated the changes over time in the temperatureof permanent magnets housed within a guide sleeve in the “opposingmagnet pole surface method”, being a disk type configuration.

FIG. 7 is a diagram comparing the changes in temperature over timewithin the guide sleeve during braking in a drum type and a disk typeconfiguration. The temperatures were measured on the surface of thepermanent magnets opposing the drum or disk. The results in the diagramcompare drum type and disk type eddy current braking apparatus withequivalent brake torque, that is with equivalent heat generation. As forthe symbols in the diagram, “To” indicates the initial temperature ofthe permanent magnets, “T” indicates the internal temperature of thepermanent magnets, “Tdmax” indicates the maximum temperature of thepermanent magnets in the drum type apparatus, “t” indicates the brakingtime, and “tend” indicates the time when braking stopped.

The results in FIG. 7 show that even if there is no difference inbraking torque between the apparatus, because a structure can be usedfor a guide sleeve in a disk type apparatus which enables effectivecooling in contact with the open air, temperature rise of the permanentmagnets can be controlled. As a result, it is possible to reduce thedistance between the permanent magnets and the brake disk, and even ifthe magnetic circuit is constructed without using a ferromagnetic body(pole piece), it is possible to secure sufficient braking torque.

Accordingly, the following is an example of the structure of a secondaspect of the present invention. The second embodiment of the presentinvention is an eddy current braking apparatus comprising: a brake diskconnected to a rotary shaft; a guide sleeve supported by a nonrotatablesection and disposed beside the brake disk; a support ring housed insidethis guide sleeve and movable in the rotary shaft direction of the brakedisk; and a plurality of permanent magnets arranged opposed to the brakedisk around the circumferential direction of the support ring, and sothat magnetic poles are opposite, wherein the permanent magnets arefreely movable in the rotary shaft direction, and the whole of the guidesleeve including the end face which opposes the permanent magnets isconstructed of nonmagnetic material.

Here, “disposed beside the brake disk” means same configuration as“disposed opposed to the brake disk”, and refers to a state in which thepermanent magnets face the braking surface (main surface) of the brakedisk.

In the eddy current braking apparatus according to the second aspect ofthe present invention, because the permanent magnets are covered by theguide sleeve including the end face opposing the permanent magnets,there is no likelihood of the magnetic pole surface of the permanentmagnets being damaged by foreign objects, or rusting due to moisture. Inthe present invention, nonmagnetic materials that may be chosen for usein the guide sleeve include aluminum, stainless steel and resin.

In addition, in the eddy current braking apparatus of the presentinvention, the guide sleeve may be constructed from a thin walledmaterial. Because this allows the weight of the whole guide sleeve to bereduced, small and light-weighted apparatus can be realized. In thiscase, by partially reinforcing the guide sleeve, the strength of theguide sleeve can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of an eddycurrent braking apparatus according to a first embodiment of the presentinvention, in a braking state.

FIG. 2 is a cross-sectional view showing the structure of the eddycurrent braking apparatus according to the first embodiment, in anon-braking state.

FIG. 3 is a diagram showing the relationship between the magneticattraction and the switching stroke during non-rotation of the brakedisk (braking state).

FIG. 4 is a diagram showing the structure of an “opposing magnet polesurface method” eddy current braking apparatus using a rotary drum asproposed in a prior application.

FIG. 5 is a diagram showing an example of a disk type eddy currentbraking apparatus as proposed in a prior application.

FIG. 6 is a diagram showing the structure of the main parts of the firstembodiment, wherein (A) is a plan view (side view) and (B) shows thecross section along the A-A′ direction.

FIG. 7 is a diagram comparing the temperature rise inside the guidesleeve in a drum type and a disk type apparatus during braking.

FIG. 8 is a cross-sectional view showing an eddy current brakingapparatus according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view showing an eddy current brakingapparatus according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view showing an eddy current brakingapparatus according to a fourth embodiment of the present invention.

-   1: Rotary shaft-   2: Brake disk-   3: Guide sleeve-   3 a: Reinforcing member-   3 b: Guide tube-   4: Support ring-   5: Cylinder, drive unit (actuator)-   6: Piston rod-   7: Permanent magnets-   8: Ferromagnetic member, magnetic pole member, pole piece-   10: Shorting sleeve-   11: Rotary drum-   12: Nonmagnetic ring

BEST MODE FOR CARRYING OUT THE INVENTION

The construction of the eddy current braking apparatus of the presentinvention is described below with reference to the drawings. FIG. 1 andFIG. 2 show an eddy current braking apparatus according to a firstembodiment of the present invention. FIG. 1 is a cross-sectional viewshowing the structure of the eddy current braking apparatus duringbraking, and FIG. 2 is a cross-sectional view showing the structure ofthe eddy current braking apparatus during non-braking.

The eddy current braking apparatus of the present embodiment includes abrake disk 2 attached to a rotary shaft 1, and a guide sleeve 3 made ofnonmagnetic material and disposed beside the brake disk 2. The guidesleeve 3 is supported by a nonrotatable section in the vehicle or thelike. A support ring 4 made of a ferromagnetic material which is movableforward and backward perpendicularly relative to the braking surface ofthe brake disk 2, that is movable towards and away from the brake disk2, is housed inside the guide sleeve 3. In addition, a cylinder(s) 5which moves the support ring 4 forward and backward are provided in theguide sleeve 3. On the other hand, pole pieces 8 made of ferromagneticmaterial are disposed on the end face of the guide sleeve 3 whichopposes the brake disk.

As shown in FIG. 6, a plurality of permanent magnets 7 are disposed atequal intervals around the circumferential direction of the surface ofthe support ring 4 which faces the brake disk 2. The magnetic polesurface of the magnets 7 opposes the braking surface of the brake disk2. The magnetic pole surfaces of adjacent permanent magnets haveopposite magnetic poles (polarity). The plurality of pole pieces 8 whichoppose the magnetic pole surface of the permanent magnets 7 are disposedso as to form pairs with the permanent magnets in the circumferentialdirection. There is no particular thickness prescribed for the polepiece, but thinner is better, and the pole piece may be constructed witha thickness of 3 mm, for example. Specifically, attachment of the polepiece can be performed by casting the ferromagnetic member as anintegrated part when molding the aluminum guide sleeve 3, for example.

The cylinder(s) 5 is disposed on the outer end wall of the guide sleeve3, as the drive mechanism for the permanent magnets. The piston rod 6passes from the cylinder 5 completely through the outer end wall of theguide sleeve to couple with the support ring 4. By using such astructure, the action of the cylinders 5 can cause the support ring 4 tomove forward and backward in the perpendicular direction relative to thebrake disk 2.

Next, the operation of the eddy current braking apparatus of the presentembodiment is described. During braking, the piston 6 of the cylinder 5moves to the right as shown by the arrow in FIG. 1, the support ringmoves forward in the perpendicular direction relative to the brake disk2, and the permanent magnets 7, opposing the bake disk 2, move towardsthe brake disk 2. In the structure in FIG. 1, an interval of 0.5 mmbetween the permanent magnets 7 and pole pieces 8 is assumed.

At this time, each permanent magnet 7 exerts magnetic lines of force onthe braking surface of the brake disk 2 via the pole piece 8. When therotating brake disk 2 intersects these magnetic lines of force, magneticinduction causes eddy current to flow in the brake disk 2, and brakingtorque is generated.

When switching to a non-braking state, the action of the cylinder 5switches, moving the support ring 4 which is connected directly to thepiston 6 to the left as shown by the arrow in FIG. 2. The permanentmagnets 7 move away from the pole pieces 8, and the magnetic lines offorce exerted by the permanent magnets 7 on the brake disk 2 weaken.With the structure of the present invention, if a switching stroke S of10 to 30 mm is secured, then hardly any braking torque is generated inthe brake disk, and magnetic leakage is not an issue.

In the examples shown in FIG. 1 and FIG. 2, a structure was used inwhich the support ring is moved by the cylinder, but the apparatus ofthe present invention is not limited to this construction, and otherdrive units which enable the support ring to move may also be used.

With an eddy current braking apparatus according to the first embodimentof the present invention as described above, because the “opposingmagnet pole surface method” is applied to a disk type braking apparatus,magnetic lines of force can be exerted on the brake disk directly fromthe magnets, resulting in excellent brake efficiency. Furthermore, thesimple structural design means a small number of components, and a lowmanufacturing cost. Moreover, because the switching stroke is small thusallowing rapid switching, a lightweight and compact apparatus can beachieved, enabling the apparatus to be installed even in a small car.

Permanent magnets are strongly temperature dependent, and theirmagnetism reduces once they reach a set temperature, reducing brakingtorque. Therefore, in order to control temperature rise of the permanentmagnets, it is necessary to leave a suitable distance between thepermanent magnets and the brake disk, which is the heat source. However,if the distance between the magnetic pole surface of the permanentmagnets and the brake disk is increased, braking torque decreases.Therefore it is necessary to provide a ferromagnetic member (pole piece)between the two to lower the magnetic resistance on the magneticcircuit, and to perform adjustment so that there is no reduction inbrake efficiency.

If the magnetic pole surface of the permanent magnets is exposed, thereis likelihood that damage by foreign objects or rust caused by moisturemay occur. The ferromagnetic member (pole piece), by covering thepermanent magnet, eliminates damage to and rusting of the magnetic polesurface. For this reason, in the eddy current braking apparatus shown inFIG. 1 and FIG. 2, ferromagnetic members (pole pieces) are provided onthe end face of the guide sleeve so as to oppose the permanent magnets.

Next, a second embodiment of the present invention is described. In thisembodiment, the entire guide sleeve which houses the permanent magnetsis made of nonmagnetic material. In this embodiment, even if aferromagnetic member (pole piece) is not provided, the magnetic lines offorce from the permanent magnets can be applied directly to the brakedisk over a short magnetic circuit length, so the efficiency of brakingtorque generation can be improved.

FIG. 8 is a diagram for describing the structure of the eddy currentbraking apparatus according to the second embodiment of the presentinvention. This eddy current braking apparatus comprises a brake disk 2attached to a rotary shaft 1, and a guide sleeve 3 made of nonmagneticmaterial, disposed beside the brake disk 2. The guide sleeve 3 issupported by a nonrotatable section of the vehicle or the like. Asupport ring 4 made of ferromagnetic material which is movable forwardand backward in the rotary shaft direction of the brake disk 2, that ismovable towards and away from the brake disk 2, is housed inside theguide sleeve 3. In addition, cylinder(s) 5 which moves the support ring4 forward and backward is provided in the guide sleeve 3. On the otherhand, the guide sleeve 3 is made of a nonmagnetic material, without aferromagnetic member (pole piece) being disposed on the end face of theguide sleeve which opposes the brake disk.

A plurality of permanent magnets 7 are provided around the support ring4 in the circumferential direction on the surface which faces the brakedisk 2. The magnetic pole surfaces of the magnets 7 oppose the brakingsurface of the brake disk 2, and the permanent magnets are arranged sothat adjacent permanent magnets have opposite magnetic poles (polarity).The guide sleeve which houses the support ring 4 and the permanentmagnets 7 is made of nonmagnetic material such as aluminum, stainlesssteel or resin. There is no particular thickness prescribed for theguide sleeve, but for the end face of the guide sleeve which opposes thepermanent magnets, thinner is better, and in the second embodiment athickness of approximately 1 mm is assumed for the end face, forexample.

The cylinder(s) 5 is disposed on the outer end wall of the guide sleeve3, as the drive mechanism for the permanent magnets. The piston rod 6passes from the cylinder 5 completely through the outer end wall of theguide sleeve to couple with the support ring 4. By using such aconstruction, the action of the cylinder 5 can cause the support ring 4to move forward and backward in the rotary shaft direction of the brakedisk 2.

FIG. 9 shows an eddy current braking apparatus according to a thirdembodiment of the present invention. In order to achieve a reduction inthe size and weight of the apparatus, in this embodiment the entireguide sleeve 3, not only the end face which opposes the permanentmagnets 7, is made of a nonmagnetic thin walled material. For example,in embodiment 2 a thickness for the guide sleeve 3 of approximately 2 mmis assumed.

The structure of other apparatus and their effects in the thirdembodiment are the same as in the second embodiment. In the thirdembodiment, because the whole of the guide sleeve 3 is constructed froma thin walled material, a reinforcing member 3 a is provided on theouter periphery of the end face of the guide sleeve 3 to maintain thestrength of the whole guide sleeve 3.

FIG. 10 shows an eddy current braking apparatus according to a fourthembodiment of the present invention. A guide tube 3 b which acts asinternal reinforcement and also as a guide is provided inside the guidesleeve 3, to obtain a double tube construction. By using a double tubeconstruction for the guide sleeve in this manner, it is possible for theguide sleeve to be even thinner walled, allowing a smaller and lighterapparatus to be achieved.

In the fourth embodiment also, the reinforcing member 3 a may beprovided around the outer periphery of the end face of the guide sleeve3 to maintain the strength of the whole guide sleeve 3.

With the eddy current braking apparatus according to the presentinvention, even if the distance between the magnets and the disk issmall, rise in the permanent magnet temperature can be controlled.Furthermore, the present invention allows sufficient magnetic flux fromthe permanent magnets to be applied to the brake disk, improving theefficiency of brake torque generation. In other words, the presentinvention does not suffer a loss of magnetic efficiency during braking,and therefore does not necessarily require the use of a ferromagneticmember (pole piece). Consequently, using a simple construction, an eddycurrent braking apparatus can be obtained which is small andlightweight, is easily installed in a vehicle and is economicallyefficient.

1. An eddy current braking apparatus comprising: a brake disk connectedto a rotary shaft; a plurality of permanent magnets arranged so thatmagnetic pole surfaces are opposed to said brake disk, and; a drivemechanism for moving said permanent magnets toward and away from saidbrake disk.
 2. An eddy current braking apparatus according to claim 1,wherein said plurality of permanent magnets is arranged so that magneticpoles of magnetic pole surfaces of adjacent permanent magnets areopposite.
 3. An eddy current braking apparatus according to claim 1,wherein said drive mechanism includes a movable support ring which holdssaid permanent magnets.
 4. An eddy current braking apparatus accordingto claim 3, further comprising a guide sleeve supported by anonrotatable structural section not connected to said rotary shaft,which receives said support ring and is disposed facing said brake disk.5. An eddy current braking apparatus according to claim 4, wherein insaid guide sleeve, ferromagnetic members are provided positioned facingsaid brake disk.
 6. An eddy current braking apparatus according to claim4, wherein a whole of said guide sleeve including an end face opposed tosaid permanent magnets is constructed of nonmagnetic material.
 7. Aneddy current braking apparatus according to claim 6, wherein said guidesleeve is formed of aluminum, stainless steel or resin.
 8. An eddycurrent braking apparatus comprising: a brake disk connected to a rotaryshaft; a guide sleeve supported by a nonrotatable section and disposedto a side of said brake disk; a support ring housed inside said guidesleeve and movable in the rotary shaft direction; a plurality ofpermanent magnets arranged opposed to said brake disk around acircumferential direction of said support ring, and so that adjacentmagnetic poles are opposite, and; ferromagnetic members disposed on anend face of said guide sleeve so as to face said permanent magnets,wherein said permanent magnets are freely movable from a position nearto and facing said brake disk, at which braking is possible, to anon-braking position away from said brake disk.
 9. An eddy currentbraking apparatus comprising: a brake disk connected to a rotary shaft;a guide sleeve supported by a nonrotatable section and disposed to aside of said brake disk; a support ring housed inside said guide sleeveand movable in the rotary shaft direction of said brake disk, and; aplurality of permanent magnets arranged opposed to said brake diskaround a circumferential direction of said support ring, and so thatmagnetic poles are opposite, and said permanent magnets are freelymovable in the rotary shaft direction of said permanent magnets, whereina whole of said guide sleeve including an end face opposed to saidpermanent magnets is constructed of nonmagnetic material.
 10. An eddycurrent braking apparatus according to claim 2, wherein said drivemechanism includes a movable support ring which holds said permanentmagnets.